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Full text of "Stomach worms (Haemonchus contortus) in sheep"

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Historic, archived document 

Do not assume content reflects current 
scientific knowledge, policies, or practices. 

Issued March 8, 1907. 

United States Department of Agriculture. 


A. D. MELVIN, Chief of Bureau. 


By B. H. Ransom, 
Chief of the Division of Zoology. 

The stomach worm of sheep, known to zoologists as Haenionchus 
contortus^ is generally recognized as one of the most serious pests with 
which the sheep raiser has to contend. Sheep of all ages are subject 
to infection, and cattle and goats as well as various wild ruminants 
may also harbor the parasite. The most serious effects of stomach- 
worm infection are seen in lambs, while full-grown sheep, although 
heavily infested, may show no apparent symptoms of disease. It is 
from these, however, through the medium of the pasture, that the 
lambs become infected. 


Among the symptoms which have been described for stomach-worm 
disease probably the most frequent are anemia, loss of flesh, general 
weakness, dullness, capricious appetite, thirst, and diarrhea. The 
anemic condition is seen in the paleness of the skin and mucous mem- 
branes of the mouth and eye, and in the watery swellings which often 
develop under the lower jaw. A more certain diagnosis may be made by 
killing one of the flock and opening the fourth stomach. The contents 
of the fourth stomach are allowed to settle gently, and by carefully 
watching the liquid the parasites, if present in any considerable num- 
bers, will be seen activelj^ wriggling about like little snakes from 
one-half to \\ inches long and about as thick as an ordinary pin. 


The worms in the stomach produce eggs of microscopic size, which 
pass out of the body in the droppings and are thus scattered broadcast 

« Some of the details in the life history of this parasite are treated more at length 
in Circular No. 93 of the Bureau of Animal Industry. 
23756— No. 102—07 


over the pasture. If the temperature is above 40° to 50° F. the e^gs 
hatch out, requiring from a few hours to two weeks, according as the 
temperature is high or low. When the temperature is below 40° F. 
the eggs remain dormant, and in this condition may retain their vitality 
for two or three months, afterwards hatching out if the weather 
becomes warmer. Freezing or drying soon kills the unhatched eggs. 
The tiny worm which hatches from the egg feeds upon the organic mat- 
ter in the manure, and grows until it is nearl}' one-thirtieth of an inch in 
length. Further development then ceases until the worm is swallowed 
by a sheep or other ruminant, after which it again begins to grow, and 
reaches maturitj^ in the fourth stomach of its host in two to three 
weeks. The chances of the young worms being swallowed ai-e greatly 
increased by the fact that they crawl up blades of grass whenever 
sufficient moisture — such as dew, rain, or fog — is present, provided 
also that the temperature is above 40° F. When the temperature is 
below 40° F. the worms are inactive. 

The young worms which have reached the stage when they are ready 
to be taken into the body are greatly resistant to cold and dryness; 
they will stand repeated freezing, and have been kept in a dried con- 
dition for thirt3'-five days, afterwards reviving when moisture was 
added. At a temperature of about 70° F. young worms have been 
kept alive for as long as six months, and the infection in inclosures 
(near Washington, D. C.) which had been pastured by infested sheep 
did not die out in over seven months, including the winter, the inclo- 
sures having been left vacant from October 25 to June 16. It is 
tmcertain whether infection in fields from which sheep have been 
removed will die out more rapidly during warm weather or during 
cold weather; experiments on this point are under way, but have not 
been sufiiciently completed for definite statements to be made. It is. 
however, safe to say that a field which has had no sheep, cattle, or 
goats upon it for a yeav will be practically free from infection, 
and fields which have had no sheep or other ruminants upon them 
following cultivation may also be safely used. The time required 
for a clean pasture to become infectious after infested sheep are 
placed upon it depends upon the temperature; that is, the field 
does not become infectious until the eggs of the parasites con- 
tained in the droppings of the sheep have hatched out and the 
young worms have developed to the final larval stage, and the ra}:idity 
of this development depends upon the temperature. It may be stated 
hei'e that neither the eggs nor the newly hatched worms are infectious, 
and only those worms which have reached the final larval stage are 
able to continue their development when swallowed. This final larval 
stage is reached in three to four da3's after the eggs have passed out 
of the body of the host if the temperature remains constantly at about 
95° F. At 70° F., six to fourteen days are required, and at 46° to 

iClr. 102] 


57° F., averaging about 50° F., three to four weeks are necessary for 
the eggs to hatch and the young worms to develop to the infectious 
stage. At temperatures below 40° F., as already stated, the eggs 
remain dormant. 


It is evident from the foregoing statements that in the northern 
part of the United States, under usual climatic conditions, infested 
and noninfested sheep umy be placed together in clean fields the last 
of October or first of November and kept there until March or even 
later, according to the weather, with little or no danger of the non- 
infested sheep becoming infected. If moved then to another clean 
field thoy may remain there nearly the entire month of April before 
there is danger of infection. From the 1st of May on through the 
summer the pastures become infectious much more quickly after 
infested sheep are placed upon them, and during May it would be 
necessary to move the sheep at the end of every two weeks, in June 
at the end of every ten days, and in July and August at the end of 
each week, in order to prevent the noninfested sheep from becoming 
infected from the worms present in the rest of the flock. After the 
1st of September the period may again be lengthened. This method 
of preventing infection in lambs would require a considerable number 
of small pastures or subdivisions of large pastures, and in many 
instances could not be profitably employed, but in cases where it could 
be used it would undoubtcdl}^ prove very effective. By the time the 
next lamb crop appeared the pastures used the year before would have 
remained vacant long enough for the infection to have disappeared, 
and would consequently again be ready for use. B3- continuing this 
rotation from year to year, not only would each crop of lambs be 
protected from infection, but as reinfection of the infested ewe flock 
is prev^ented at the same time, the parasite would in a few years be 
entirely eradicated from the flock and pastures. 

If such frequent rotation is not possible or practicable, a smaller 
number of pastures ma}' be utilized, after the ewe flock has been 
treated with vermifuges. The treatment may be given either before 
or after the birth of the lambs. If before, the ewes should be treated 
before pregnancy is too far advanced, in order to avoid possible bad 
results from the handling necessary in treatment. Probably the best 
time for treatment is late in the fall or early in the winter. The 
treated sheep should be placed immediately on clean pasture in order 
to avoid reinfection. The object of treating the ewes is to get rid of 
the worms with which they are infested, and thus remove the source 
from which the pasture becomes contaminated. If it were possible 
by treatment to free the old sheep entirely from stomach worms, it is 
evident that the lambs would remain free from infection, provided, of 

[Cir. 102] 


course, that the flock were afterwards kept on clean pasture. Unfor- 

tunatel}', there is no vermifuge known which can always be depended 
upon to remove all of the worms, hut it is possible to get rid of most 
of them and thus greatly reduce the amount of infection to which the 
lambs will bo exposed. 

Two other methods may be suggested by which lambs can be kept 
free from infection with stomach worms. 

1. It is assumed that a large pasture is available which has had no 
sheep, goats, or cattle upon it for a year, if a permanent pasture, or 
since cultivation, if a seeded pasture. This pasture is subdivided 
into two by a double line of fence, and a drainage ditch is run along 
the alle^' between the two fences. At one end of the alley between 
the two subdivisions a small yard is constructed, communicating with 
each of the subdivisions by means of a gate. When the lambs are 
born they are placed in one of the subdivisions and the ewes are placed 
in the other. The small yard should be kept free of vegetation and 
must not drain into the lamb pasture. As often as necessary the lambs 
are allowed in the small yard with the ewes for suckling. The rest 
of the time the lambs and ewes are kept separate in their respective 
pastures. Bj' this arrangement the lambs are exposed to infection 
on\y while they are in the small yard, where they may become infected 
either by embryos of the stomach worm present on the luanure-soiled 
skin of the infested ewes, or by embryos picked up from the ground 
which has been contaminated b}' the droppings of the ewes. The 
chances of infection from the skin of the ewe are so slight that in 
practice this source of infection need not be considered. The danger 
of infection from the ground may be avoided by frequently removing 
the manure from the yard and keeping the surface sprinkled with 
lime and salt. The lambs and ewes will soon learn the way to their 
proper pastures, and after a few days little difficulty will be experi- 
enced in separating them each time after the lambs are through 

2. Another plan which may be followed where the climatic condi- 
tions are suitable — that is, in regions where there is a cold winter sea- 
son — is that of having the lambs born at a time of year when there 
will be no danger of their becoming infected during the suckling 
period, and weaning and separating them from the rest of the flock 
before the advent of warm weather. Under the usual climatic condi- 
tions of the State of Ohio, for instance, if the lambs are born in the 
latter part of October or the first of November they may remain with 
the ewes on fields which have not been previously occupied by sheep, 
goats, or cattle within a j'ear — or, if cultivated fields, since cultiva- 
tion — until the following March without danger of becoming infected, 
since the eggs in the droppings of the infested ewes will not hatch 
out during this time of year because of the cold weather. The use of 



fields not previously occupied by sheep, goats, or cattle within a year, 
or since cultivation, is necessary, since otherwise the fields would be 
already infected with young worms which had hatched out and reached 
the infectious stage before the beginning of cold weather, and the 
lambs would consequently be liable to infection from picking up these 
young worms, which are not killed by cold weather after they have 
reached the final stage of larval development. When they are weaned 
the lambs must, of course, be placed on clean pasture, if they are to 
continue free from infection. With this method only two clean pas- 
tures are necessary, one in which the ewes and lambs are placed in the 
fall, and another for the lambs when they are weaned in March. 

Unfortunately for this scheme, it is not always possible to have 
lambs born at the beginning of the winter season; but with additional 
clean pastures a modification of the foregoing method may be used in 
the case of lambs born toward the end of the winter or in the spring. 
In the northern United States lambs born the first of February, for 
example, may be kept with their mothers in a clean field or pasture 
until the last of March, as in the case of those born at the beginning 
of winter, but unlike the latter they will not then be old enough to 
wean. Accordingly thej^ are not separated from the rest of the flock, 
but the ewes and lambs are moved together to a second clean pasture 
April 1. May 1 thej^ are moved to a third clean pasture, May 15 they 
are moved again, and finally the lambs are weaned June 1 at the age 
of four months, and moved by themselves to a clean pasture. In the 
case of lambs born the first of March and weaned the first of July 
three additional clean pastures would bo required for use during the 
month of June, and with later lambs a still greater number of pastures 
would be necessary. 


Among the remedies which ma}' be used to remove stomach worms 
may -be mentioned coal-tar creosote, bluestone, and gasoline. 

The animals to be treated should be deprived of feed for twelve to 
sixteen or even twenty-four hours before they are dosed, and in case 
bluestone is used should receive no water on the day they are dosed, 
either before or after dosing. In drenching, a long-necked bottle or 
a drenching tube may be used. In case a bottle is used the dose to be 
given may be first measured ofl^, poured into the bottle, and the point 
marked on the outside of the bottle with a file, so that subsequent 
doses may be measured in the bottle itself. A simple form of drench- 
ing tube consists of a piece of rubber tubing about 3 feet long and 
one-half inch in diameter, with an ordinary tin funnel inserted in one 
end and a piece of brass or iron tubing 4 to 6 inches long and of 
suitable diameter inserted in the other end. In use the metal tube is 
placed in the animal's, mouth between the back teeth, and the dose is 
poured into the funnel, which is either held by an assistant or fastened 

[Cir. 102] 

• 6 

to a post. The flow of liquid through the tube is controlled by pinch- 
ing the rubber tubing near the point of union with the metal tube. 
It is important not to raise the animal's head too high on account of 
the danger of the dose entering the lungs. The nose should not be 
raised higher than the level of the eyes. The animal may be dosed 
either standing on all fours or set upon its haunches. It has been 
found by experiment that if the dose is taken quietly most of it will 
pass directly to the fourth stomach when the animal is dosed in a 
standing position, and that when the animal is placed on its haunches 
onl}' a part of the dose passes iiiuiiediatelj' to the fourth stomach. 
From this it is evident that the position on all fours is preferable, as 
more of the dose passes to the place where its action is required. 

Great care should be used not only in dosing to avoid the entrance 
of the liquid into the lungs, but also in the preparation and adminis- 
tration of the remedy so that the solution may not be too strong or 
the dose too large. 


Good results have been obtained from a single dose of a 1 per cent 
solution of coal-tar creosote. This solution is made by shaking 
together 1 ounce of coal-tar creosote and 99 ounces (6 pints 3 ounces) 
of water. The doses of this 1 per cent mixture recommended by 

Stiles areas follows: 

Lambs 4 to 12 months old 2 to 4 ounces. 

Yearling sheep and above 3 to 5 ounces. 

Calves 3 to 8 months old 5 to 10 ounces. 

Yearling steers _ 1 pint. 

Two-year-olds and above 1 quart. 

Serious objections to the use of coal-tar creosote have been found in 
that the substance known by this name varies considerably in compo- 
sition and in that some trouble is often experienced in obtaining it in 
many parts of the country. Complaints have been made that the 
substance dispensed by some druggists as coal-tar creosote has failed 
to give satisfactory results. 


Bluestone, or copper sulfate, has been extensively used in South 
Africa in the treatment of sheep for stomach worms and is recom- 
mended by the colonial veterinary surgeon of the Cape Colony as the 
best and safest remedy. His directions are to take 1 pound avoirdu- 
pois of pure bluestone, powder it fine, and dissolve in 42 whisky- 
bottlefuls (9i United States gallons) of warm water. It is better to 
lirst dissolve the bluestone in 2 to 4 bottlefuls of boiling water, then 
add the remaining quantity in cold water, and mix thoroughly. This 
solution is given in the following-sized doses: 

Lambs 3 months old J ounce. 

Lambs 6 months old 1 i ounces. 

Sheep 12 months old 2^ ounces. 

Sheep 18 months old 3 ounces. 

Sheep 24 months old Si ounces. 

[Cir. 102] 


In making up the solution only clear blue crystals of bluestone 
should be used. Bluestone with white patches or crusts should be 
rejected. It is especially important that the bluestone and water be 
accurately weighed and measured, and that the size of the dose be 
graduated according to the age of the sheep. 


Gasoline is one of the most popular remedies for stomach worms 
which has been used in this country and has the particular advantage 
of being readily obtained. It is important to repeat the dose if the 
gasoline treatment is"employed, and it is usual to administer the treat- 
ment on three successive days, as follows: 

The evening before the first treatment is to be given the animals 
are shut up without feed or water and are dosed about 10 o'clock the 
next morning. Three hours later they are allowed feed and water, 
and at night they are again shut up without feed or water. The next 
morning the second dose is given, and the third morning the third dose, 
the treatment before and after dosing being the same in each case. 

The sizes of the doses are as follows: 

Lambs } nunce. 

Sheep 5 ounce. 

Calves h ounce. 

Yearling steers 1 ounce. 

The dose for each animal is measured and mixed separately in 
linseed oil, milk, or flaxseed tea, and administered by means of a 
bottle or drenching tube. Gasoline should not be given in water. 


Many other remedies in addition to those mentioned here have been 
used in the treatment of stomach-worm disease with more or less 
success. Several of the coal-tar dips on the market are recommended 
by the manufacturers for the treatment of worms, and the action of 
some of them is much the same as that of coal-tar creosote. 

It is not the policy of the Department to recommend the use of an^- 
particular proprietary remedy, and as the action of some such agents is 
very uncertain it is suggested that, if it is desired to use them, the}' 
be used with caution and only in accordance with the printed directions 
on the package. Whatever remedy is used, it is wise to test it on two 
or three animals before the entire flock is dosed. 


James Wilson, 

Secretary of Agriculture. 

Washington, D. C, FSruary 8, 1907. 

ICir. 102]